The invention relates to a circuit arrangement for feeding electrical users with a DC voltage wherein at least one user is connected via a switch controller to a feed circuit fed with an impressed current. The switch controller contains a switch element controllable by a control circuit dependent on the DC voltage directly fed to the user or fed to the user via a voltage converter.
Such a circuit arrangement is already disclosed in German OS No. 32 42 023, incorporated herein by reference.
The known circuit arrangement serves the purpose of remotely feeding electrical users, whereby the remote feed current held constant is first converted into a constant voltage in the circuit arrangement preceding the user, and then is transformed in potential-separated fashion to the desired user voltage. Since the circuit arrangement can match its input voltage to the respectively required power, it functions in a very low-loss manner. When the circuit arrangement is overloaded at the user side, then the input voltage drops, as does the possible power consumption. The circuit arrangement is thus comparatively secure against damage due to too high a load.
Investigations in the framework of the invention, however, have shown that it is desirable in some cases to bridge a possible overload at a certain time with maximum power output. Such a situation particularly exists when the circuit arrangement has a plurality of outputs and users operating at these outputs which have a constant power consumption given changing voltage. Under such pre-conditions, a power-wise overload at one of the outputs can lead to a general collapse of the output voltage. When, as a consequence, the user which caused the overload is disconnected from the output allocated to it, then the other users, none-the-less, take increased current at the voltage which is then reduced. When the input voltage of the circuit arrangement has dropped in the meantime, then the increased current can no longer be output under certain conditions, although the sum of the power is lower than that which the circuit arrangement can output as a maximum during operation. In this fashion, the output voltage can finally collapse so that the circuit arrangement can no longer operate the users which are still intact per se.
On the other hand, it can occur in special cases given a circuit arrangement of the type initially cited that the input voltage is boosted to such an extent due to an overload at the output, that the constant current source switches into a voltage limiting condition, and the input current of the DC-DC converter drops. This can lead to stability problems, or to the disconnection of the constant current source.